The aim of this pilot study was to calculate the disability-adjusted life years (DALY) as a quantification of the burden of myocardial infarction (MI) attributable to road-traffic noise in Belgrade, Serbia. Exposure to road-traffic noise was estimated on a sample of almost 6000 adult inhabitants living in the central municipality Stari Grad in Belgrade, Serbia. Each participant was assigned to daytime noise levels for 16 h exposure measured on the street of current residence. Population-attributable fraction of MI due to road-traffic noise was calculated based on the distribution of the population in different noise exposure categories and the respective relative risk of MI compared to the reference level. DALYs due to noise-related MI were calculated as the sum of years of life lost and years with disability. The contribution of road traffic noise to the occurrence of MI for the population of the municipality Stari Grad in Belgrade equals 2.518%. Total DALY for MI due to road-traffic noise results in 176 years, that is, 115 years for men and 61 years for women. When adjusted for the present size of the population in Belgrade, total DALY due to road-traffic noise equals 107 years/million inhabitants that is, 70/million inhabitants for men and 37/million inhabitants for women. The burden of disease due to road-traffic noise in Belgrade is relatively small but noteworthy from the public health point of view.

Keywords:Disability-adjusted life years, myocardial infarction, noise, transportation, years of life lost, years lost due to disability

Environmental noise presents a large public health problem in many countries. Back in 2009, Serbia implemented the law on the protection from environmental noise, [1] harmonized with the European Union Directive 2002/49/EC relating to the assessment and management of environmental noise. [2] The law and its amendments oblige authorities to create noise maps for agglomerations above 250,000 inhabitants by June 30, 2015, as well as for agglomerations above 100,000 inhabitants by June 30, 2020. [1],[3] At the same time, the estimated population of Serbia was 7,320,807 inhabitants. [4] The country is divided into 25 administrative regions; 9 out of 25 regions are inhabited by more than 250,000 persons. Within these administrative regions, the cities of Belgrade, Novi Sad, Kragujevac and Niš can be defined as urban agglomerations according to the directive 2002/49/EC. Consequently, the first round of noise mapping should take place in these cities. Until date, however, noise mapping of any city in Serbia is still at the planning stage.

Disability-adjusted life years (DALY) is a population-related indicator of the burden of disease, measuring the gap between current health status and an ideal health situation where the entire population lives to an advanced age, free of disease and disability. [5] DALY is calculated as the sum of the number of life years lost due to premature death (years of life lost [YLL]) and the number of years lived with disability due to a given disease or condition or its consequences (years lost due to disability [YLD]). [5],[6] One DALY can be interpreted as one lost year of healthy life. Key advantages of DALY are that it combines the quantity of life (premature death) with the quality of life (time spent with disability) and that it helps compare various risk factors and diseases with the burden of disease. [7]

Global and regional burden of disease was estimated for many diseases, [8] as well as for some environmental factors, including unsafe water, sanitation and hygiene, [9],[10] indoor smoke, [11] and outdoor air pollution. [12] As for environmental noise, World Health Organization (WHO) has recently published two guidelines for risk assessment and quantification of the burden of disease in relation to noise exposure. [5],[13]

Given the lack of official estimations of the burden of disease from noise in Serbia, we have decided to undertake a pilot study in a small urban area, which may initiate similar large-scale assessments in the selected urban agglomerations. The aim of this study was to calculate DALY as a quantification of the burden of myocardial infarction (MI) attributable to road-traffic noise in Belgrade, Serbia. Facing the lack of noise maps for Belgrade we had to extrapolate noise exposure in a single urban municipality of Stari Grad to the whole population of Belgrade.

Methods

Noise exposure assessment

Exposure to road-traffic noise was estimated on a sample of almost 6000 inhabitants living in a single municipality of Belgrade, Serbia. The down-town municipality of Stari Grad is characterized by the predominance of road traffic over other sources of urban noise. According to census data, the municipality population is about 55,000 adults. Adult residents of every 10 th apartment in all streets were approached by distributing questionnaires to post boxes inside the buildings according to the list of dwellers. The sampling was conducted from 2004 to 2009. In total, 11,420 questionnaires were distributed, and 6049 were filled out and returned (response rate 52.9%). Persons who failed to report their current address or basic socio-demographic data (n = 188) were excluded from the study. The final sample, therefore, comprised 5861 participants, 2598 men, and 3263 women aged 42.9 ± 17.9 years.

Noise levels were measured in the middle of 118 streets of this municipality during September-October 2008. A hand-held noise level analyzer type 2250 Brüel and Kjær was used, according to recommendations of the International Standard Organization for the measurement of community noise (ISO, 1982). Noise measurements were performed on working days. Equivalent noise levels (Leq) were measured in two intervals during the daytime (between 8 and 10 am, and between 2 and 4 pm), and in one evening interval (between 6 and 8 pm). Noise level meter was positioned on the pavement by the road; the time interval of each measurement was 15 min; the speed of sampling was 10/s, with 9000 samples collected per measurement at one site. From the obtained Leq levels, the composite 16-h daytime noise level (Leq 16h [decibel - the unit of A-weighted sound pressure level [dBA]) was calculated for each street. Each participant was assigned to daytime Leq 16h values measured at the street of current residence.

Calculation of the population-attributable fraction for myocardial infarction due to road-traffic noise

The population-attributable fraction (PAF) was calculated based on the distribution of the population in different exposure categories and the respective relative incidence of disease. The method was adapted from the guidelines for the estimation of the burden of disease from environmental noise proposed by the WHO. [5],[14]

First, the exposure-response function [Equation 1] was applied to calculate odds ratios (OR) for the occurrence of MI in relation to Lday 16h daytime noise. [5],[14],[15] The OR is an estimate of the population relative risk (RR).

Second, the attributable risk percentage (AR%) among the population exposed to a given noise level range was calculated according to the Equation 2, based on the OR (RRs) for all exposure categories.

AR% = [(RR−1)/RR]100 [%] (Equation 2)

Third, PAF for MI due to road-traffic noise was calculated from the proportion of the population in each exposure category i (Pi) and the RR (RRi) at each exposure category i compared to reference level, according to Equation 3. [5],[14]

PAF = [Σ (Pi RRi) −1]/ Σ (Pi RRi) (Equation 3)

Calculation of disability-adjusted life years

Newly diagnosed cases and deaths from MI in Belgrade in 2010 by gender and age groups were obtained from the Serbian Acute Coronary Syndrome Registry. [16] In 2010, the total number of newly diagnosed cases of MI was 4083 (2536 men and 1547 women), and the total number of deaths due to MI was 1189 (699 men and 490 women). [16]

First, total YLL were calculated by multiplying the number of deaths from MI for each age category (N) with the standard life expectancy at age of death, or average loss of life years per death due to MI (L) [Equation 4]. [6]

YLL = N L (Equation 4)

In order to calculate the average years lost due to premature death from MI, we relied on the average life expectancy of the population in Serbia, reported by the Institute of Public Health of the Republic of Serbia. [4] The estimated life expectancy in Belgrade is 71.89 years for men, and 77.18 years for women. Therefore, total YLL were calculated for men and women separately. Furthermore, YLL due to road-traffic noise were calculated by multiplying total YLL with PAF.

Second, YLD due to road-traffic noise were calculated by multiplying the number of non-fatal cases of MI attributable to road-traffic noise (I) with disability weights (DW) and average duration of disability (L), according to Equation 5. [6]

YLD = I DW L (Equation 5)

The number of non-fatal cases attributable to road-traffic noise (I) was calculated by multiplying total number of non-fatal cases of MI with PAF. Total number of non-fatal cases of MI was obtained by subtracting the number of deaths from MI from the number of newly diagnosed cases from MI, in order to avoid double counting of cases. Disability weight is an index in between 0 and 1 indicating the severity of the disability associated with the health condition. For the purposes of this study, a DW of 0.405 was applied, in accordance to WHO guidelines. [5] Average duration of disability was fixed at 1, to calculate data for each year of life.

Finally, to estimate the DALYs lost due to noise-related MI in Belgrade, YLL and years with disability due to road-traffic noise were added, according to the following formula [Equation 6]. [5],[6],[7],[8],[9],[10],[11],[12],[13],[14]

DALY = YLL + YLD (Equation 6)

Taking into account the size of Belgrade population in 2010, [16] the obtained DALY values were further adjusted per million inhabitants.

Results

[Table 1] presents the estimated exposure to road-traffic noise, RR and attributable fraction for MI. The study reveals that almost 65% of the population of Stari Grad is exposed to noise levels <60 dBA for 16 h daytime exposure. These persons are considered being at no risk from the development of MI due to road-traffic noise. On the other side, persons exposed to higher noise levels are at some risk from MI. [Table 1] shows that 3% of the inhabitants exposed to noise ranging from 60 to 64.9 dBA (almost 20% of the population of Stari Grad) are at high risk of developing MI due to noise. Nevertheless, 27% of the inhabitants exposed to noise above 75 dBA (<0.5% of the population of Stari Grad) are at increased risk of developing MI when compared with the unexposed persons.

Table 1: Estimated road-traffic noise exposure, population relative risk and attributable fraction for myocardial infarction for the city of Belgrade

The resulting contribution of road traffic noise to the occurrence of MI for the population of Stari Grad, Belgrade equals 0.025176 or 2.518%.

[Table 2] presents the calculation of DALY from MI due to road-traffic noise in the investigated area. In total, 73 non-fatal cases of MI and 30 deaths from MI can be attributed to road-traffic noise in Belgrade in 2010. Persons with non-fatal MI due to road-traffic noise (46 men and 27 women) are expected to live with a disability for almost 30 years. Persons who died from MI due to road-traffic noise (18 men and 12 women) lost 146 years of life. The average number of years lost due to noise-related MI was 4.89 for the whole sample, that is, 5.45 years for men and 4.09 years for women. Total DALY due to road-traffic noise results in 176 years, that is, 115 years for men and 61 years for women. When adjusted for the present size of the population in Belgrade, total DALY due to road-traffic noise equals 107 years/million inhabitants, that is, 70/million inhabitants for men and 37/million inhabitants for women [Table 2].

Table 2: Calculation of DALY from myocardial infarction due to road-traffic noise in Belgrade by gender

To the authors' knowledge, this is the first estimation of the burden of disease from environmental noise in Serbia. The Institute of Public Health in Serbia conducted a large-scale study on the burden of disease and injury in Serbia in 2000. [17] They reported that ischemic heart disease (IHD) (including MI) was the leading cause of burden of disease among men (18.1 DALY/1000 population); at the same time, it was the third largest contributor to the burden of disease among women (7.9 DALY/1000 population). [17] At that time, several risk factors were studied in relation to burden of disease, such as obesity, physical inactivity, hypertension, high blood cholesterol, smoking and alcohol consumption; environmental factors (air pollution, water quality, noise), however, were not taken into consideration. [17]

Later on, Janković et al. reported similar estimations of the burden of disease in Serbia for 18 diseases and conditions. [18] According to their assessment, IHD contributed to 26.1 DALYs per 1000 population in men, and to 14.1 DALYs per 1000 for women. [18] Using PAF for road-traffic noise, we extrapolated these data to 652.5 DALYs from IHD per million inhabitants among men and to 352.5 DALYs from IHD per million inhabitants among women attributable to road-traffic noise. When compared with the presented extrapolations, DALYs from MI obtained in our study are substantially smaller. The differences arise primarily from the fact that IHD comprises several forms of cardiovascular diseases (stable angina, unstable angina) that may not necessarily display in the form of MI.

Most recently, Šipetić et al. (2013) published population-ARs of IHD due to several lifestyle factors in Serbia. [19] The most important risk factors for IHD were physical inactivity (contributing to 21326 DALYs for men and 15183 DALYs for women), hypertension (18429 DALYs for men, 13554 DALYs for women), cigarette smoking (21635 DALYs for men, 6208 DALYs for women), overweight (14101 DALYs for men, 8414 DALYs for women), high blood cholesterol (6573 DALYs for men, 2986 DALYs for women), and inadequate intake of fruit and vegetables (4461 DALYs for men, 1993 DALYs for women). [19]

Our results show that the contribution of noise to the burden of IHD is considerably smaller when compared with other major factors. We are aware that environmental noise does not present such a large public health problem as do obesity, diet, hypertension or physical inactivity. However, the above-mentioned factors are not the only preventable risk factors; exposure to environmental noise can be modified by adequate public health measures, such as insulation, regulation of transport, and strict adherence to noise regulations.

The PAF of 2.5 % calculated in this pilot study is similar to assessments in other countries, that is, Germany. [5] Other estimations of the transportation noise burden of disease were reported in the Netherlands and in Belgium. De Hollander et al. estimated that between 390 and 1020 cases of IHD per million inhabitants per year were attributable to road-traffic noise, and that the annual number of DALYs ranged from 110 to 295 years/ million inhabitants. [7] Stassen et al. reported that between 1304 and 3377 cases of IHD in 2004 were attributable to environmental noise. [20] They computed that between 456 and 1182 DALYs or between 77 and 199 DALYs/million inhabitants were attributable to road-traffic noise. [20] In comparison to the two presented studies, our estimations of DALYs for MI are considerably smaller. We hypothesize that the investigated populations were exposed to different noise levels and that there may be other unidentified population-related factors that affect the occurrence of the disease.

The limitations of our pilot study arise from the applied sampling procedure. First, the estimated noise exposure in the municipality of Stari Grad may differ from noise exposure in other parts of Belgrade. Being an administrative center of the city, Stari Grad may be noisier than other municipalities in Belgrade. Once noise maps for the whole city become available, we should estimate noise exposure for the whole population more precisely. To the best of authors' knowledge, there are no official comparisons between short-term noise measurements and long-term noise indicators in Belgrade. On the other side, we were not able to estimate the burden of disease in this single municipality, because the data on mortality and morbidity from MI were cumulative for the whole city. Second, we may have over-estimated the role of road-traffic noise over other noise sources (aircraft noise, railway noise), particularly in other parts of the city. Third, we were not able to take the whole population of Serbia into account, primarily due to the lack of noise exposure data. Fourth, we were not able to estimate the cost of burden of MI. For example, in the United Kingdom, the cost of cases of MI, stroke and dementia attributable to daytime noise levels ≥55 dBA was around £1.09 billion. [21] Fifth, for the purposes of the study, we assumed that the relationship between noise exposure and the occurrence of MI was causal. In reality, the association between noise and cardiovascular health is not straightforward, and is modified by physiological and psychological reactions to noise, that is, noise annoyance. [22] From the public health point of view, however, objective noise pollution is of prime importance when calculating burden of disease and it accounts for other personal modifiers of noise exposure. Sixth, we were not able to estimate the role of air pollution, another well-known environmental factor for IHD. [23] Recent systematic review supports the hypothesis that noise and air pollution act independently on cardiovascular health. [24] Finally, our study provides no evidence of long-term effects of noise, which makes it inadequate for generalization and future predictions. [25]

Nevertheless, we find that the presented study points to the magnitude of the problem of road-traffic noise in Belgrade from the perspective of DALY as acknowledged indicator of the burden of disease, rather than from the simple exposure-effect point of view. We would like to raise the awareness of road-traffic noise and to encourage public health authorities to perform more precise and continuous estimations of the burden of disease attributable to noise and other environmental factors in Serbia. Such studies would help policy makers assess the scope of current environmental problems, identify populations at risk, and initiate adequate population-oriented interventions. [6]

Conclusion

This pilot study identified that 2.5% of all cases of MI among the population of the municipality of Stari Grad in the center of Belgrade may be attributable to road-traffic noise. The estimated burden of MI due to road-traffic noise over 60 dBA in Belgrade 2010 equals 176 DALYs, or 107 DALYs per million inhabitants. The burden of disease due to road-traffic noise in Belgrade is relatively small, but may be noteworthy from the public health point of view.

Acknowledgments

The study was financially supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, project No. 175078.